A typical high-pressure sodium arc discharge lamp has an arc tube mounted within a light-transmissive outer envelope. The mounting of the arc tube may include one or more welds for mechanical and electrical integrity. While this type construction is effective, it is expensive because the welding process, particularly where multiple welding operations are required, is difficult to automate. See U.S. Pat. No. 2,951,959, issued Sep. 6, 1960, to Fraser et al., applying broadly to any type of electric discharge device involving a double-enveloped construction.
As explained in U.S. Pat. No. 3,094,640, issued Jun. 18, 1963, to Gustin, relating to the construction of high-pressure electric discharge lamps, each spot weld affords an opportunity for imperfection in lamp construction and, consequently, it may be desirable to reduce the number of such welds where a feasible alternative construction technique is available.
U.S. Pat. No. 4,287,454, issued Sep. 1, 1981, to Feuersanger et al., illustrates a high-pressure sodium lamp with two arc tubes mounted by a construction which may include multiple spot welds. The number of welds required for mounting two arc tubes in a lamp typically is double or higher than that required in a single arc tube counterpart. There is also the requirement for precision alignment of the two arc tubes, usually in a parallel arrangement. See U.S. Pat. No. 4,689,518, issued Aug. 25, 1987, to King.
It would be an advancement of the art if a support for mounting one or more arc tubes within the outer envelope of a high-pressure sodium lamp were available where the support is weldless and well adapted to automated construction techniques.